Device for controlling boost pressure in an internal combustion engine

ABSTRACT

An arrangement includes a first controller which is only switched through to an actuator for a turbocharger if a fault recognition device detects no fault in the operation of the engine. A switchover is made from the first controller to a second controller, if the fault recognition device detects a critical fault. In this connection, the second controller receives a system deviation as an input signal that is different from the one received by the first controller. Thus in the event of a fault, the turbocharger can be controlled in a very flexible manner without the danger that the speed of the turbocharger is increased into its critical range.

FIELD OF THE INVENTION

The present invention relates to an arrangement for controlling theboost pressure of an internal combustion engine which has a turbochargerin its at least one exhaust line and an actuator that acts on theturbocharger and is controlled by a first. The first controller is onlyswitched through to the actuator when a fault detection device detectsno fault in the operation of the engine.

BACKGROUND OF THE INVENTION

In boost pressure control, it may occur that a fault in the operation ofthe internal combustion engine (e.g., a combustion miss) or faultysensors (e.g., air pressure sensor, air mass flow sensor) causes thespeed of the turbocharger to be adjusted upward into a critical rangeand the turbocharger is permanently damaged as a result. German PatentNo. 195 13 156 describes that this problem occurs, in particular, ininternal combustion engines having two rows of cylinders with oneturbocharger each. If one of the two turbochargers is in fact defectiveor a catalytic converter is clogged in one of the two exhaust lines, thecontrol circuit will balance the system deviation of the actual boostpressure value from the setpoint boost pressure value caused by thefault occurring on one side by increasing the speed of the turbochargeron the side without a fault. In doing so, the speed of the turbochargercan reach a critical value, resulting in permanent damage to theturbocharger. In order to preclude permanent damage to a turbocharger inthe event of a fault, as described in German Patent No. 195 13 156, theclosed-loop control is switched off and a switchover is made to anopen-loop control if a fault recognition device detects a fault in oneside of the two exhaust gas lines. The open-loop control is designed insuch a way that the speed of the turbocharger is not increased into itscritical speed range. In contrast to closed-loop control, the actualvalue of charge air or air mass no longer has an influence on thecontrol signal for the turbocharger in the event of a fault in open-loopcontrol. The open-loop control limits the speed of the turbocharger to aconstant value. In many types of faults, this value represents anoverreaction in limiting the speed of the turbocharger to a constantvalue.

A control device for an internal combustion engine is described in U.S.Pat. No. 5,497,751, which provides two controllers for the control ofthe ignition and/or fuel injection for the individual cylinders. Theidentical input variables, which are provided by separate sensors, aresupplied to both controllers so that both controllers make the samecontrol information available to the ignition and/or injection device ofthe internal combustion engine. The control device therefore has asecond controller in order to increase the reliability in an engine usedin an airplane.

The objective of the present invention is to provide an arrangement thatreacts with flexible control of the turbocharger in the event of afault.

SUMMARY OF THE INVENTION

The object is attained in that a first controller which controls theturbocharger when no fault exists is switched off and a switchover ismade to a second controller when a fault is detected in the operation ofthe engine. In this connection, the second controller receives a systemdeviation as an input signal that is different from the one received bythe first controller boost pressure measured by an air pressure sensorin the intake path on the pressure side of the turbocharger serves as anactual value for the first system deviation and an air mass measured inthe intake path on the suction side of the turbocharger serves as anactual value for the second system deviation. With such an arrangement,the control of the turbocharger can be adapted in an essentially moreflexible manner to the type of the fault present than with a rigidcontrol of the turbocharger.

A control signal suitable for the turbocharger in the case of a fault isproduced by superimposing a precontrol signal on the output signal ofthe second controller. It is advantageous to make the precontrol signaldependent on the type of fault.

The fault recognition device should be capable of recognizing a greatvariety of signals. For example, it monitors the sensors required forthe boost pressure control and/or an existing lambda control for errorsand/or it detects combustion misses and signals a fault if a specificmiss rate is exceeded.

In an internal combustion engine having two rows of cylinders with twoturbochargers, both turbochargers are controlled simultaneously, aswitchover taking place from the first to the second controller if thefault detection device detects a fault in the area of one of the tworows of cylinders.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE shows a block circuit diagram illustrating the function of anarrangement for controlling the boost pressure of an internal combustionengine according to the present invention.

DETAILED DESCRIPTION

An internal combustion engine having two rows of cylinders 1 and 2 isassumed in the exemplary embodiment shown in the drawing. Each of thesetwo rows of cylinders 1 and 2 is equipped with a turbocharger 3 and 4.Tubocharger 3 has a turbine 5 in the exhaust channel of first row ofcylinders 1 and a compressor 6 coupled with it in the intake channel. Inthe same manner, a turbine 7 of second turbocharger 4 is arranged in theexhaust channel of second row of cylinders 2 and compressor 8 coupledwith it is arranged in the intake channel. Turbines 5 and 7 of the twotubochargers 3 and 4 are each equipped with a bypass valve 9 and 10 in aconventional manner. It is possible to control the boost pressureproduced by each of turbochargers 3, 4 to a specific value via thesebypass valves 9 and 10. Compressors 6 and 8 of the two turbochargers 3and 4 feed their charge air into a common intake channel 11 in which athrottle valve 12 and an air pressure sensor 13 for the measurement ofthe boost pressure are located. At the output of throttle valve 12,intake channel 11 branches to the two rows of cylinders 1 and 2.

An actuator 14, a pulse valve, for example, activates the two bypassvalves 9 and 10 of turbochargers 3 and 4 simultaneously. The boostpressure of the two turbochargers 3 and 4 can also be controlled via thegeometry of turbines 5, 7 instead of bypass valves 9 and 10.

Inputs E1, E2 . . . En of a fault recognition device 15 are connected toperipheral units of the internal combustion engine in order to be ableto detect their malfunctions. Of particular significance are themalfunctions described below. The malfunctions result in a criticalspeed increase of one or both turbochargers 3, 4. Fault recognitiondevice 15 should therefore be capable of recognizing faults thatoriginate from a boost pressure sensor 13, a boost pressure sensor 17arranged in intake manifold 16, a lambda control (not shown) or acontrol loop fault. In addition, fault recognition device 15 should becapable of recognizing misfires in both rows of cylinders 1 and 2 andsignal a fault if the misfire rate exceeds a specified limit value. Thefault recognition may in addition extend to injection valve faults andfaults in the ignition system. Also, an empty tank should be recognizedas well as active injection blank-out periods.

In general, all faults which for any reason (e.g., catalytic converterfault on one side, turbocharger fault on one side, excessive misfirerate on one side, etc.) result in the speed of one of the twoturbochargers 3, 4 being increased into a critical range must bedetected.

If fault recognition device 15 does not recognize a fault, it places aswitch 18 into such a position that an actual boost pressure value LDImeasured by air pressure sensor 13 is switched through to a node 19 inwhich the stored actual boost pressure value LDI is determined inrelation to a setpoint boost pressure value LDS, which is specified by asetpoint generator 20. Setpoint generator 20 is a characteristics mapdependent on throttle valve position DK (or the gas pedal position) andengine speed N.

The system deviation between actual boost pressure value LDI andsetpoint boost pressure value LDS present at the output of node 19 issupplied to a first controller 21 (e.g., a PDI controller). If there areno faults, fault recognition device 15 switches an additional switch 22into such a position that output signal LR1 of first controller 21arrives at the input of actuator 14. In such absence of a fault, theboost pressure of the two turbochargers 3 and 4 is thus controlled by aclosed loop circuit having first controller 21.

If fault detection device 15 has now detected a fault, it moves switch18 into a second position so that in place of the actual boost pressurevalue LDI measured by air pressure sensor 13, an air mass measured by anair mass sensor 17 is now supplied to node 19. A model actual boostpressure value MLI can be determined from the measured air mass in acontact unit 23 and this model actual boost pressure value MLI is thensupplied to node 19.

While air pressure sensor 13, which supplies the actual value of a firstsystem deviation determined for first controller 21, is arranged in theintake path on the pressure side of turbocharger 3, 4, air mass sensor17, which supplies the actual value of a second system deviationspecified for second controller 24, is arranged in the intake path onthe suction side of the turbocharger.

The output signal of node 19, which indicates the storage of the actualvalue delivered directly by the air mass sensor 17 or the storage of themodel actual boost pressure value MLI rather than the setpoint boostpressure value LDS, arrives at a second controller 24, which ispreferably a P controller but also may be a PD or PID controller, forexample. In a node 25, a precontrol signal VS is superimposed on outputsignal LR2 of second controller 24 in a node 25. This precontrol signalVS is formed in a contact unit 26 as a function of engine speed N andsetpoint boost pressure LDS.

Fault recognition device 15 can report to precontrol 26 the type offault recognized via a fault signal FS so that the precontrol generatesa precontrol signal VS as a function of the type of fault.

Signal LRV originating in node 25 by the superimposition of controlleroutput signal LR2 and precontrol signal VS is switched through toactuator 14. For this purpose, fault recognition device 15 moves switch22 into the appropriate position. The second control loop including thesuperimposed precontrol prevents the speed of either of turbochargers 3,4 from being increased into its critical speed range due to a fault. Inparticular, if one of the two turbochargers of a pair of turbochargersaccording to the embodiment is defective or a clogged catalyticconverter in one of the exhaust lines brings about a system deviation onone side, the other turbocharger is prevented from attaining thesetpoint boost pressure value by its speed being increased above itscritical speed range.

The above-described switchover from a first control to a second controlmay also be used to protect the turbocharger of an internal combustionengine with only one row of cylinders in the event that the firstcontrol might increase the speed of the turbocharger to an unacceptablerate due to a fault.

What is claimed is:
 1. An arrangement for controlling a boost pressureof an internal combustion engine, comprising: at least one turbochargerarranged in at least one exhaust line of an internal combustion engine;an air pressure sensor arranged in an intake path on a pressure side ofthe at least on turbocharger, the air pressure sensor measuring a boostpressure; an air mass sensor arranged in an intake path on a suctionside of the at least on turbocharger, the air mass sensor measuring anair mass; an actuator acting on the at least on turbocharger; a faultrecognition device; a first controller receiving a first systemdeviation as an input signal, the first controller being switchedthrough to the actuator only when the fault recognition device detectsno fault in an operation of the internal combustion engine that iscritical for the at least one turbocharger, an actual value of the firstsystem deviation being the boost pressure; and a second controllerreceiving a second system deviation as an input signal, a switchoverbeing made from the first controller to the second controller when thefault recognition device detects a critical fault, an actual value ofthe second system deviation being the air mass.
 2. The arrangementaccording to claim 1, wherein: in the event of a fault, a control signalfor the actuator is generated by superimposing a precontrol signal on anoutput signal of the second controller.
 3. The arrangement according toclaim 2, wherein: the precontrol signal is a function of the type offault.
 4. The arrangement according to claim 1, wherein: the faultrecognition device monitors the air pressure sensor and the air masssensor for faults.
 5. The arrangement according to claim 1, wherein: thefault recognition device monitors a lambda control for faults.
 6. Thearrangement according to claim 1, wherein: the fault recognition devicedetects combustion misses.
 7. The arrangement according to claim 1,wherein: the internal combustion engine has two rows of cylinders andtwo turbochargers; the actuator acts on the two turbochargerssimultaneously; and the switchover takes place if the fault recognitiondevice detects a fault in an area of one of the two rows of cylinders.